The invention relates to a negative-working radiation-sensitive mixture which contains as essential constituents
a) a compound which forms a strong acid when irradiated, PA1 b) a compound having at least two reactive groups which can be crosslinked by an acid and PA1 c) a water-insoluble binder which is soluble or at least swellable in aqueous-alkaline solutions. PA1 (a) a compound which forms an acid under irradiation, PA1 (b) a compound containing at least two reactive groups which can be crosslinked by an acid, and PA1 (c) a water-insoluble binder which is soluble or at least swellable in aqueous-alkaline solutions,
The invention furthermore relates to a radiation-sensitive recording material produced therefrom, which is suitable for the production of photoresists, electronic components or printing plates or for chemical milling.
In UV lithography, the resolution limit is determined by the wavelength of the radiation used. The constant reduction in structural dimensions, for example in chip production, therefore requires different lithography techniques in the submicron range. High-energy UV light or electron beams and X-rays, for example, are used because of their short wavelength. However, the change in the lithography techniques manifests itself in a change in the requirements of the radiation-sensitive mixture. A summary of these requirements is given, for example, in the paper by C. G. Willson "Organic Resist Materials-Theory and Chemistry" (Introduction to Microlithography, Theory, Materials, and Processing, Publisher L. F. Thompson, C. G. Willson, M. J. Bowden, ACS Symp. Ser., 219, 87 (1983), American Chemical Society, Washington). There is therefore an increased demand for radiation-sensitive mixtures which are preferably sensitive within a wide spectral range and accordingly can be used in conventional UV lithography or, without losses in sensitivity, in the advanced technologies, such as, for example, the mid- or deep-UV, electron beam or X-ray lithography.
Negative-working radiation-sensitive mixtures which contain bisazides as crosslinking agents and isoprene derivatives as binders are known and have been used in the past for the preparation of photoresists for printing plates, printed circuits and integrated circuits. However, their use in microlithography in particular is limited by various technical disadvantages: it is difficult to produce faultless high-quality layers without defects (pin-holes); the heat stability of such mixtures is inadequate, so that distortions in reproduction may occur during processing due to thermal flow of the mixtures, and finally their resolving power is limited to structures greater than 2 .mu.m, since they tend to undergo swelling to an undesirably high degree, even in the hardened regions, during the necessary development with organic solvents, which in turn manifests itself in distortions in the structure or inhomogeneous development processes and therefore inadequate reproduction of the precision of the patterns of a mask.
For the above-mentioned reasons, other negative-working radiation-sensitive mixtures have been proposed, which can be irradiated with radiation of shorter wavelength, for example high-energy UV, electron or X-ray radiation, to allow generation of structures finer than 2 .mu.m.
Such a material consists, for example, of a copolymer or mixture of glycidyl methacrylate and 2,3-dichloropropyl methacrylate (DCOPA). In this material also, the glass transition temperature is inadequate for many applications but in particular its low resistance to plasma etching is at fault. This material must moreover also be processed with developers which contain organic solvents and are not very environment-friendly. The low resistance to plasma etching described above is a problem which also applies to other known negative-working photoresists based on aliphatics.
EP-A 0,164,248 has thus proposed an acid-hardenable mixture which can be developed under aqueous-alkaline conditions, has an improved resistance to plasma etching due to the use of aromatics and is sensitive towards near UV light (350-450 nm). Compounds which have been proposed as being suitable for generating acid in this mixture are, in particular, sulfonic acid ester derivatives of diazonaphthoquinone, which form weakly acid carboxylic acids when exposed to light and therefore have to be used in comparatively high concentrations. However, because of the weak absorptions of the photolytic acid donor and its inadequate bleaching properties, and also their low sensitivity in the deep UV, such mixtures are unsuitable for uses in this range and also for electron and X-ray radiation.
U.S. Pat. No. 3,692,560 describes the combination of an acid-hardenable mixture based on an acid-crosslinkable melamine derivative, a novolak and chlorinated benzophenones as photolytic acid donors. These mixtures also do not have an adequate sensitivity in the deep UV range. The photolytic formation of hydrogen halide acids as the crosslinking catalyst is moreover undesirable, since these typically can undergo reactions with the doping agents during the subsequent doping processes. The hydrogen halide acids which remain in the hardened resist are furthermore highly corrosive and may lead to destruction of the material which can be imaged and the production equipment.
The same applies to the derivatives, mentioned in EP 0,232,972, of the acid generator DDT claimed in that patent, which is highly toxic and for this reason alone does not seem to be appropriate in practice. However, a considerable sensitivity in the deep UV range (200-300 nm) can nevertheless be achieved with such compounds.
Further compounds (a) which can be characterized as photolytic acid donors and have hitherto been recommended are, in particular, onium salts, such as diazonium, phosphonium, sulfonium and iodonium salts, of non-nucleophilic acids, for example of HSbF.sub.6, HAsF.sub.6 or HPF.sub.6 (J. V. Crivello, Polym. Eng. Sci., 23, 953 (1983)), halogen compounds (EP-A 0,232,972, DE-A 1,572,089 (=GB-A 1,163,324), DE-A 1,817,540 (=U.S. Pat. No. 3,615,455), DE-A 1,949,010 (=U.S. Pat. No. 3,686,084), DE-A 2,317,846 (=GB-A 1,381,471 and 1,381,472) and U.S. Pat. No. 3,912,606), in particular trichloromethyltriazine derivatives (DE-A 1,298,414 (=GB-A 1,234,648), DE-A 2,243,621 (=GB-A 1,388,492), DE-A 2,306,248, DE-A 2,718,259 (=U.S. Pat. No. 4,189,323), DE-A 3,333,450 (=S.A. 84/7165) DE-A 3,337,024 (=U.S. Pat. Nos. 4,619,998 and 4,696,888), and also U.S. Pat. Nos. 3,515,552, 3,536,489 and 3,615,630), or trichloromethyl-oxadiazole derivatives (DE-A 2,851,472 (=U.S. Pat. Nos. 4,212,970 and 4,232,106), DE-A 2,949,396 (=U.S. Pat. No. 4,279,982), DE-A 3,021,590 (=U.S. Pat. No. 4,371,607) and DE-A 3,021,599 (=U.S. Pat. No. 4,371,606) and DE-A 3,333,450), o-quinonediazide sulfochlorides or organometallic-organohalogen combinations.
These compounds have been recommended in some cases in negative-working and in some cases in positive-working radiation-sensitive materials. However, the use of such photolytic acid donors involves certain disadvantages which drastically limit their possible uses in various fields of application. Thus, for example, many of the onium salts are toxic. Their solubility is inadequate in many solvents, which results in the choice of the coating solvents being limited. Undesirable foreign atoms are moreover in some cases introduced when onium salts are used, and these can lead to disturbances in the process, especially in microlithography. They furthermore also form highly corrosive Bronstedt acids during photolysis, and these render the use of radiation-sensitive mixtures containing them on sensitive substrates unsatisfactory. As already mentioned earlier, the halogen compounds and the quinone-diazide sulfochlorides also form highly corrosive hydrogen halide acids. Such compounds furthermore have only a limited stability on certain substrates, which in accordance with the doctrine of DE-A 3,621,376 (=U.S. Pat. No. 4,840,867) was improved in the past by inserting an intermediate layer between the substrate and the radiation-sensitive layer containing compounds of type (a), although this leads to an undesirable increase in defects and a reduction in the reproducibility of the process.
Recent works by F. M. Houlihan et al., SPIE 920, 67 (1988) have shown with the aid of positive-working systems that, in addition to the above-mentioned acid donors, nitrobenzyl tosylates which form sulfonic acids of little mobility when exposed to light can also be used in certain resist formulations which are unstable to acid. It can be deduced from these results that such compounds can also be used for photohardenable systems. However, the sensitivities achieved with these and the heat stability of the photoresists have proved to be inadequate.
In spite of the numerous inventions and improvements in this field, no material is currently known which suggests heat-stable radiation-sensitive negative-working mixtures which can be developed under aqueous-alkaline conditions and in which a high sensitivity in the deep UV range, by means of low-corroding photolytically generated acids, is linked with a high resolution.
Because of the disadvantages described, there is therefore a need for further photolytically acting acid donors which, as constituents of radiation-sensitive mixtures, do not have the disadvantages described above and thus have a sufficient reactivity and acid strength to cause compounds of type (b) to crosslink even during short exposure times.